The project seeks to specify how odor intensity, and in particular the psychophysical function that relates perceived intensity to concentration, depends upon the physicochemical nature of odorous stimuli and upon various conditions of odor masking and adaptation. The odor stimuli will include odorous pollutants, irritants, and masking agents. Particular experiments aim: 1) To obtain psychophysical functions for various odorous substances and to relate the parameters (e.g. growth rate) of the functions to the physicochemical properties and perceived qualities of the substances. 2) To study observers who lack common chemical sensitivity in one nasal passage in order to isolate thereby the contribution of trigeminal stimulation to overall odor intensity. 3) To formulate a quantitative description of how various masking odors modify the psychophysical function; to specify in particular the masking ability of ozone. 4) To determine how adaptation alters the psychophysical function; to specify the trading relation between intensity and duration of adapting stimuli. 5) To chart the course of adaptation in observers who lack common chemical sensitivity. 6) To determine the degree of adaptation and masking that occurs when the adapting or masking stimulus is presented to one nostril and the test stimulus to the other nostril.